Masaki Yotsumoto, a second-year high school student, had been told by his remarried father that he was going to have a younger stepsister. But when he finally met her, it turned out to be none other than Chloe Nanase, a girl from his own class.

Chloe, with her blonde hair, petite frame, and voluptuous figure, is one of the most well-known beauties at school. Masaki had been trying to figure out how to build a good sibling relationship with her now that they were family—but then he accidentally sent a half-asleep message saying, “Let’s be happy together.”

A younger sister unaware of her own feelings × a brother trying to keep things sibling-like—

This is a sweet and frustrating romantic comedy about two awkward people gradually coming to understand each other.